A framework for implementing a spatial stock assessment for the Heard Island and McDonald Islands Patagonian toothfish (Dissostichus eleginoides) fishery in Division 58.5.2

There has been concerted efforts on increasing understanding of both the spatial structure of Patagonian toothfish as well as the characteristics of the longline tagging dataset available for the Heard Island and McDonald Island (HIMI) Patagonian toothfish fishery in Division 58.5.2.  This paper continues to progress this work by responding to recommendations from WG-SAM-2025 to explore additional data visualisations and summaries, presenting results from the distributional regression tree approach as a means of clustering spatial areas based on analysis of toothfish length-bin frequency data, presenting three initial spatial area scenarios from which to develop initial spatially structured integrated assessment models for HIMI toothfish and providing a framework for implementing a two-area integrated stock assessment model for Patagonian toothfish at HIMI. Work is also in progress to develop a spatial stock assessment in RTMB that uses a Spatial-Brownie tag-recapture model with the aim to better reflect the spatial patterns in HIMI toothfish tagging data.